1. Field of the Invention
The present invention relates to a resist surface modifying liquid for use as a surface treatment liquid before a post exposure baking (PEB) step of a resist film, and a method for forming a resist pattern using the same.
2. Related Art
In lithographic techniques, for example, steps of: forming a resist film constituted with a resist material on a substrate; conducting selective exposure by irradiating the resist film with radiation such as an electron beam or light through a mask having a formed certain pattern; and subjecting to a developing treatment, whereby a resist pattern having a certain shape is formed, are carried out.
As micro-fabrication of semiconductor elements proceeds, shortening of the wavelength of the light source and increase in the numerical apertures (higher NA) of the projection lens proceed. At present, exposure devices with NA of 0.84 have been developed using an ArF excimer laser having a wavelength of 193 nm as a light source. As light sources having shorter wavelengths is used, improvement of lithography characteristics such as sensitivity to the light sources for exposure, resolution property to allow patterns of minute size to be reproduced, and the like is demanded for the resist material. As a resist material that meets such requirements, a chemically amplified resist containing a base resin having a solubility in an alkaline developer that will be altered by the action of an acid, and an acid generator that generates acid upon exposure has been used.
As one of the procedures for further improving the resolution property, a lithographic method, liquid immersion lithography generally referred to (hereinafter, may be also referred to as “liquid immersion exposure method”), has been known in which exposure (immersion exposure) is carried out while allowing a liquid (liquid for liquid immersion exposure) having a refractive index greater than that of the air to exist between the sample and an objective lens of the exposure device (see, e.g., Nonpatent Document 1).
Regarding the liquid immersion exposure method, it is reported that a high resolution similar to those exhibited in the case in which a light source with a shorter wavelength and in the case in which a high NA lens is used can be achieved even though a light source with the same exposure wavelength is used, and also reported that a decrease in the focal depth width is not found. Additionally, the liquid immersion exposure method can be carried out using a preexisting exposure device. Therefore, the liquid immersion exposure method is expected to be capable of realizing formation of a resist pattern with a high resolution and also with favorable focal depth width at low costs. Thus, in production of semiconductor elements in which a large capital investment is required, the liquid immersion exposure method has drawn attention as a method that greatly influences on semiconductor industry in terms of costs, as well as lithography characteristics such as resolution, etc.
Meanwhile, attention has been focused on characteristics such as water repellency and transparency of fluorine-containing compounds in recent years, and research and development in various fields have been extensively conducted. For example, in the field of resist materials, an acid labile group such as a methoxymethyl group, a tert-butyl group, or a tert-butyloxycarbonyl group is introduced into a fluorine-containing polymer compound at present, for use as a base resin of positive chemically amplified resist compositions. However, when such a fluorine-based polymer compound is used as a base resin of a positive resist composition, disadvantages such as generation of a large quantity of out-gas after the exposure, and insufficient resistance against dry etching gas (etching resistance), and the like may occur.
Recently, a fluorine-containing polymer compound having an acid labile group having a cyclic hydrocarbon group has been reported as a fluorine-containing polymer compound that is superior in etching resistance (for example, see Nonpatent Document 2). In addition, a fluorine-containing polymer compound for imparting water repellency to a resist film in a resist composition for liquid immersion exposure has been reported (for example, see Nonpatent Document 3).
Nonpatent Document 1: Proceedings of SPIE, Vol. 5754, pp. 119-128 (2005)
Nonpatent Document 2: Proceedings of SPIE, Vol. 4690, pp. 76-83 (2002)
Nonpatent Document 3: Journal of Photopolymer. Sci. Technol., Vol. 19, No. 4, pp. 565-568 (2006)